My sister is taking advantage of my mom?

shes a grown woman and needs to look after her own kids like it or not, her husband has a job and is providing so she should look after the kids if they are hers, my older sister who is 25 was just like this until my mom finally kicked her out and we havent spoken to her since that was about a year ago, im only 16 and even i was sticking up for my mom u need to do the same your mom is getting older and doesnt need this sort of thing, i know your sister might be really nasty and arguementative (if shes anything like my sister) and might make a big drama out of it but you need to be firm about this cos itll just keep getting out of hand.